1. Field of the Invention
The present invention relates to a card-mounting rack for electronic part-mounting cards for mounting parts of the card type such as electronic circuit boards for construction of a computer system or the like in high density into a housing.
2. Description of the Related Art
Conventionally, when a plurality of parts of the card type (a part of the type mentioned is hereinafter referred to merely as card) such as electronic circuit boards on which electronic parts are mounted are accommodated into the inside of a housing of a standardized rack such as a 19-inch rack or the like to construct a system such as a computer system, such a conventional method as disclosed in Japanese Patent Laid-Open No. 10-178289 and U.S. Pat. No. 5,868,585 is used. According to the method, a mother board is mounted in the inside of a housing such that it extends in parallel to the side faces of the housing but perpendicularly to the bottom face of the housing. Further, a plurality of cards are mounted only on one face or side of the mother board such that they extend in parallel to the bottom face of the housing. In such a mounting method as just described, the cards are connected to the mother board only in a limited one direction. Therefore, the length of a cable necessary for connection between the cards increases as the number of cards to be mounted onto one mother board increases. Such increase of the length of a connection cable between cards as just described makes a cause of signal delay, noise increase and so forth. As a result, it becomes a factor that the performance of the entire system is degraded.
In order to suppress such degradation of the system performance arising from increase of the length of a connection cable between cards as just described, the following method may be used. In particular, in order to reduce the length of a connection cable between cards, a mother board is placed at the center of a housing such that it extends in parallel to the side faces of the housing but perpendicularly to the bottom face of the housing and a plurality of cards are mounted on both faces of the mother board provided at the center of the housing such that they extend in parallel to the bottom face of the housing. However, according to such a mounting method as just described, the size of cards is limited by the width of the housing, and a card having a size generally used for the 19-inch standard rack cannot be mounted.
Also another method may be used wherein, in order to prevent occurrence of such a limitation to the size of the cards as just described, a mother board is placed at the center of a housing such that it extends perpendicularly to the side faces and the bottom face of the housing and a plurality of cards are mounted on both faces of the mother board provided at the center of the housing such that they extend in parallel to the bottom face of the housing.
However, in such mounting methods as described above, an air flow for cooling generated in the inside of the housing of a rack or the like by sucking air from the front face of the housing and exhausting air to the rear face of the housing is intercepted by the mother board provided at the center of the housing. This gives rise to a problem that the cooling system does not sufficiently function. A method wherein air is sucked from a lower portion of a housing and exhausted from an upper portion of the housing may be used as alternate measures without using the general cooling system of the front face air sucking and rear face air exhausting type described above. However, in the cooling system of the bottom face air sucking and top face air exhausting type, it is necessary to assure a space for the location of cooling fans above and below cards to be mounted. Therefore, when a system such as a computer system is constructed, the height of a housing of a rack or the like becomes greater than that of a housing of a standard rack or the like and the mounting density of electronic parts other than a mother board and cards to be mounted in the housing decreases. As a result, a problem occurs that improvement of the performance of the entire system by high-density mounting and miniaturization is obstructed.